The molecular changes associated with the transition of melanoma cells from Radial Growth Phase (RGP) to Vertical Growth Phase (VGP) and the acquisition of the metastatic phenotype is not very well-defined. Recent work from this laboratory demonstrated that this transition is associated with loss of nuclear expression of AP-2a in metastatic melanoma cells which resulted in deregulation of c-KIT, MCAM/MUC18, MMP-2, and VEGF, all of which are involved in the progression of human melanoma. However, the mechanisms for the lack of AP-2a expression in metastatic melanoma cells are not known. Using melanoma tissue microarrays combined with LSC and AQUA technologies, here, we further validated the lack of nuclear AP-2a expression in metastatic melanoma cells. In an effort to search for other target genes regulated by AP-2a, we have identified the thrombin receptor (PAR-1) and provided evidence for inverse correlation between AP-2a and PAR-1 expression in metastatic melanoma cells. Regulation of PAR-1 by AP-2a was demonstrated in vitro and in vivo, thus providing a unique link between the coagulation system and the progression of human melanoma. The role of PAR-1 in the progression of human melanoma is now established through the efforts of this continued research. We have used stable silencing of PAR-1 by lentiviral shRNA combined with cDNA chip arrays and cytokine membrane arrays to identify possible downstream genes regulated by the axis of thrombin/PAR-1. These genes include MCAM/MUC18, Connexin 43, Maspin, RUNX3, IL-8, Ang-2, GRO, ACRP30, and GITR-ligand. The hypothesis to be tested in this proposal is that loss of nuclear AP-2a results in upregulation of PAR-1 and contributes to the acquisition of the malignant phenotype in human melanoma. To test this hypothesis, we now propose: 1) To determine the mechanism(s) for the loss of nuclear AP-2a expression during melanoma progression;2) To investigate how the axis of thrombin/PAR-1 contributes to the metastatic phenotype;and 3) To inhibit PAR-1 expression in vivo via delivery of siRNA packaged in neutral liposome nanoparticles as a possible new therapeutic modality. It is expected that the results obtained from this study will provide a better understanding of the role of AP-2a and PAR-1 in the progression of human melanoma that could thereby lead to new modalities to inhibit melanoma metastasis. PUBLIC HEALTH RELEVANCE: The molecular changes that are associated with the progression of human melanoma from radial growth phase into a vertical growth phase (metastatic phenotype) are largely unknown. Previously, we identified that the loss of the transcription factor AP-2a is associated with this transition. In this grant application, we will continue to investigate the role of AP-2a and its downstream target gene, the thrombin receptor (PAR-1), in the progression of human melanoma.